New clones, having issues

[kerogirl420]

So I have some new clones that have been growing for about 3 weeks now. This is my first grow and my clones have rooted well. For the last week or so, I have been having slight problems with my leaves loosing color. The tips on my plants are yellow on all leaves and one plants top stems are purple. I seem to have good lighting and ventilation in my grow box, but could be wrong. My plants seem to be growing very slowly however one is going better than the other. Could anyone please give me advice on how to correct any issues I am doing wrong.

 

[kerogirl420]

I also only water every few days but mist the leaves at lights out. I use a 18/6 light sequence. I have tried doing an extra feeding at the beginning of the week as well as adding Epsom salt due to another leaf that was yellow with brown spots not shown in the pics. I have read through countless forums trying to pinpoint this but I can't. Please help

 

[Coke420]

What's the ph of the water

 

[kerogirl420]

The pH is reading around 6.8. The only time the water is used immediately is for feeding otherwise all spraying is done with water that has sat overnight in spray bottle

 

[Jimmycricket]

They are just hungry for nitrogen is all.